1. Field
The present disclosure relates to casting of prefabricated concrete products with a substantially horizontal slipform casting, where concrete mass is fed through a restricted cross-section, which restricted cross-section proceeds along with the casting.
2. Description of Related Art
Prefabricated concrete elements and products, such as hollow-core slabs and solid concrete slabs, are conventionally cast as slipform casting on elongate casting beds in a continuous casting process. The length of said continuous casting process is defined either on the basis of the combined length of the elements to be cast, or on the basis of the maximum length of the casting bed. The length of casting beds used in slipform casting can be up to 150-200 m, depending on the size of the element factory. After the slipform casting equipment has cast a continuous slab on the casting bed, the cast concrete mix is allowed to cure on the casting bed. When the concrete mix is cured, the uniform cast concrete slab is sawed in predetermined lengths on the basis of the targets of usage of the final elements, and the sawn concrete elements are lifted off the casting bed to storage, to wait for transportation to their respective locations of usage.
In slipform casting devices, concrete mix is fed either in one or several stages to a casting mold moving along with the casting device, said mold being formed by side walls of the mold and vibrating beam defining the top surface of the mold, together with the casting bed. The side walls and vibrating beam of the casting mold perform a vibrating and/or trowelling compacting motion for compacting the concrete product. When casting hollow-core slabs, the slipform casting device is provided with means for forming the cavities. Generally a slipform casting device is a casting machine moving on a stationary casting bed along with the casting process, but a slipform casting device can also be realized as a stationary casting station, in which case the casting bed moves along with the casting process with respect to the casting station.
One of the most common types of slipform casting devices is an extruder. In an extruder-type slipform casting device, the concrete mix is fed on feed screws that extrude the concrete mix under pressure to the slipform casting mold. Thus, in an extruder-type casting device, the feeding of the concrete mix to a slipform casting mold is carried out in one single feed step. When casting hollow-core slabs, at the end of the feed screws is attached hollow-core forming members, such as hollow-core mandrels.
The form of the slipform cast product is defined by the restricted cross-section, i.e. the slipform casting mold, formed in an extruder by the top surface of the casting bed, and side plates and top trowelling plate. Thus the top trowelling plate of the slipform casting mold defines the shape of the upper surface of the product to be cast.
In the present day buildings and constructions the requirements for concrete elements vary greatly, which include their shapes also. Due to the compaction effect of the slipform mold in slipform casting, the change of the shape of the cross-section of the product to be cast from the normal rectangular is problematic.